Heretofore, polyimide-based and polybenzoxazole-based resins having excellent heat resistance and electrical insulation properties have widely been used in a surface protective film and an interlayer dielectric film of semiconductor device, an insulating layer of organic electroluminescence elements, a flattened film of TFT substrates, and the like. When a coating film of a polyimide precursor and a polybenzoxazole precursor is thermally cyclodehydrated to obtain a thin film having excellent heat resistance and mechanical properties, firing at a high temperature of about 350° C. is usually needed.
However, due to requirements such as reduction of thermal load and achievement of low warpage for devices, there has recently been required a positive photosensitive material which is curable by firing at a low temperature of about 250° C. or lower, and more preferably 200° C. or lower, and also has high sensitivity and high resolution.
A low-temperature curable resin composition includes, for example, a photosensitive resin composition in which a ring-closed polyimide, a photo acid generator, and a heat crosslinking agent having a methylol group are used (Patent Literature 1). However, the photosensitive resin composition had a problem such as large warpage because of high elastic modulus and high shrinkability during curing.
Photosensitive resin compositions in which a polyimide or polybenzoxazole precursor including an aliphatic introduced therein and a photo acid generator are used (Patent Literatures 2 and 3) could achieve low elastic modulus, but film shrinkage due to dehydration ring closure leads to large warpage. Therefore, low warpage could not be realized even in the case of the photosensitive resin compositions in which these resins are used. Furthermore, in order to realize low warpage, there is disclosed a water-soluble photosensitive composition comprising a multi-component block copolymerization polyimide resin having an average molecular weight of 20,000 to 200,000, including a specific diamine residue and acid dianhydride residue, a photosensitizer, and water (Patent Literature 4). However, the water-soluble photosensitive composition has poor exposure sensitivity because of using a material for achieving low linear expansion property and also has restricted uses because of containing a large amount of water, and thus the composition cannot be used in a surface protective film and an interlayer dielectric film of semiconductor devices, an insulating layer of organic electroluminescence elements, and the like. Meanwhile, a negative-type photosensitive composition comprising a soluble polyimide including an aliphatic diamine introduced therein, a photopolymerizable compound, and a photopolymerization initiator has been proposed (Patent Literature 5). However, the negative-type photosensitive composition could not satisfy resolution required for use as a surface protective film of semiconductor devices.